Drill bit for drilling over-size hole



P. W. KOONTZ DRILL BIT FOR DRILLING OVER-SIZE HOLE March 15, 1955 Filed July 2. 1951 IN V EN TOR.

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TTQQNE Y5 United States Patent DRILL BIT FOR DRILLING OVER-SIZE HOLE Pierce W. Koontz, Los Angeles, Calif.

Application July 2, 1951, Serial No. 234,764

Claims. (Cl. 255-319) The present invention relates generally to earth-boring tools of the type used in drillingoil wells and the like, and more particularly to a rotary drill bit having cutters rotatably mounted upon a shank member in such a way that the bit is adapted to drill an over-size hole. This is accomplished without having any bodily movement of the cutters radially outward in order to enlarge their effective cutting range. By an over-size hole is meant a hole having a diameter larger than the nominal or physical size of the drill bit which in the normal bit is the maximum size of the hole produced.

Many attempts, with varying degrees of success, have been made to design a bit able to drill an over-size hole. A bit of this character has many advantages, some of which are given below. These advantages can generally be measured or expressed in terms of drilling costs since the cost per foot of hole drilled is closely watched in all operations and provides a convenient and reliable index of the drilling efficiency of a bit or other tool involved in producing the finished well.

As a drill bit is used to drill a hole, the cutting elements are worn away so that their nominal size is decreased and the diameter of the hole produced gradually decreases. As a result, the well bore tapers slightly with the sides converging gradually toward the bottom. If the hole drilled is equal to the size of the bit, then a new full size bit cannot be run in the hole to the bottom of the well drilled by an old bit. Under these circumstances it may require reaming the sides of the hole to enlarge the bore to a uniform diameter in order that a new bit may be run in the full distance to the bottom of the existing hole. This extra operation of reaming is not required with a bit which can drill a hole appreciably larger than the nominal diameter of the cutting elements.

When the diameter of the hole produced does not exceed the nominal diameter of the cutting elements, it is possible for a bit to bind or hang up in the hole, that is, it gets wedged into the formation. On the other hand, if the diameter of the hole produced is larger than the nominal size of the bit, the bit is always free running. Not only can it be raised and lowered easily at all times but it also consumes less power in drilling since less energy is lost in uselessly scraping the sides of the hole.

A bit capable of drilling an over-size hole produces a larger hole for a given size of bit. In many instances this means that a bit has a longer useful life since, even though the cutting elements are worn down, the diameter of the hole drilled is greater than the nominal diameter of the worn cutters and remains longer in excess of the minimum permissible bore size.

It is the usual practice to reach a stage of drilling operations at which a drill bit is lowered through casing set in the well, the maximum physical dimension of the bit thus being limited by the inside bore of the casing. With a conventional type of bit the largest hole which can be produced below the casing is then equal to the internal diameter of the casing; but a bit able to produce an over-size hole can drill a hole that is larger than the inside diameter of the casing. As a result, there is a great reduction in the amount of underreaming required to enlarge the hole sulliciently to permit the casing to be extended downwardly without reduction in diameter; and in some cases underreaming may be eliminated entirely.

All these advantages are of prime importance to users of drill bits since the longer life and greater usefulness of a bit results not only in an increased amount of drilling "ice accomplished with each tool but in a marked reduction in the number of times the tool has to be changed for a given distance drilled. Since modern wells are normally relatively deep, a great deal of the time required to drill a well to a given depth may be spent in changing tools. It often requires several hours to make a round trip, that is raise the drill stem to remove a drill bit or other tool and then run the drill stem back into the bore hole with a new tool on the end of it. It is not uncommon for the time required to make a round trip for the purpose of changing tools to exceed greatly the useful drilling life of a bit in the hole. From this it becomes self-evident that any increase in the drilling efficiency of a bit which allows a particular bit to drill farther or faster in comparison with other bits results in a greatly preferred tool because the economics from a saving in time spent changing bits can be greater than those directly from the increase in footage per bit.

Thus it becomes a general object of my invention to produce a drillbit of the type that inherently drills an oversize hole.

Thus it is also an object of my invention to provide a drill bit producing an oversize hole in which there is no bodily movement of the cutters radially outward to extend their cutting range in order to increase the size of the hole produced.

it is also an object of my invention to produce a rotary bit for drilling an oversize hole and having rotatably mounted cutters with cutting elements of a type adapted to drill in relatively hard formations, the axis of revolution of the cutters being fixed relative to the shank of the bit.

Another object is to provide a bit that is simple in construction in order to furnish the required strength and be relatively simple to make.

A further object is to provide a bit in which wearing surfaces are on removable or easily replaceable parts and eliminated from the main parts of the shank that are diflicult or expensive to replace.

These objects have been attained in a bit constructed according to my invention by providing cutter bearing means mounted upon a drill shank, and rotatably supporting the cutters to revolve about an inclined axis intersecting, or substantially so, the vertical longitudinal axis of the shank at an acute angle so that the axis of the bearing means extends downwardly away from the shank axis. The two cutters are disc-shaped with cutting elements around their periphery. These cutters revolve in parallel planes perpendicular to the axis of the cutter bearing and therefore inclined to the vertical. One of the cutters lies substantially entirely at one side of the shank axis and engages the earth at the bottom of the drilled hole at a position spaced toward said one side from the shank axis in order to establish a central axis for the drilled hole that passes through said position of cutter engagement. As a result the bit rotates about an axis which is eccentric to or spaced from the shank axis and drills an over-size hole. The amount of over-size is approxlmately twice the eccentricity or ofiset between the vertical shank axis and the axis of the hole as established by said one cutter.

In a preferred design of bit, the two cutters are each provided with ball races on both sides, as are also fixed bearing plates. The races hold a number of ball bearings that provide means to take both radial and end-wise bearing loads. The cutter mounting pin is thus relieved of the chief source of wear and its life is greatly increased, while at the same time an effective and eificient bearing is provided for rotatably supporting the cutters on the pm.

A drill bit according to my invention resembles in some ways the drill bit shown in Fisher Patent 2,133,022 issued Oct. 11, 1938; but it is an improvement thereon. The bit of the Fisher patent drills a hole of the same size as the cutters and has no tendency to drill an oversize hole as does the present invention.

The above objects and advantages of my invention, as well as others not specifically referred to, have been attained in a manner which will be better understood by reference to the following description and to the annexed drawings, in which:

Fig. 1 is a vertical median section through a drill bit constructed according to my invention;

Fig. 2 is a combined section and elevation taken on line 2-2 of Fig. 1; and

Fig. 3 is a bottom view and section taken on line 3-3 of Fig. 1.

The drill bit illustrated in Figs. 1 and 2 comprises a shank having on its upper end a threaded pin 11 by which the bit is adapted for attachment in a conventional manner to a drill stem, the lower end of which is shown at 12. The bit is attached to the drill stem so that its longitudinal axis AA, which is normally vertical or generally so, coincides with the axis of the drill stem. It will be understood that when in the following description directional terms such as horizontal or vertical are used, these terms are used in a relative sense for descriptive purposes and refer to the bit when in the position of Fig. 1 which is the normal position for drilling a well bore; but such terms are not to be construed as limitative upon the invention since the longitudinal axis of the drill bit may often be in an inclined position while drilling.

Shank 10 has an internal cavity 14 through which circulating fluid flows. The cavity is closed at one side by inclined plate 15 which is welded along its edges to the shank. At the upper and lower ends of inclined plate 15 are located short horizontal plates 16 and 17 respectively which are welded to the shank and to the inclined plate. In this way the internal cavity in the shank body is sealed off. One or more nozzles 18 and 19 are located in plates 16 and 17 respectively to direct circulating fluid out of the shank onto and around the cutting elements described later. In this way the velocity of the circulatin fluid is utilized to wash the cutting elements clean of adhering particles of earth. Although shank 10 is herein shown and described as being of what may be termed a built-up construction it will be realized that the entire shank may be cast in one piece, making such changes in its construction as will be understood by persons skilled in the art.

Cavity 14 is made as large as possible inside the shank in order to obtain a maximum reduction in velocity of circulating fluid passing through the bit and a corresponding reduction in erosion or scour of the shank from the fluid. At high velocities this erosion is substantial. But by making cavity 14 of maximum cross-section, fluid velocity is lowered and the life of the bit is lengthened. For most of its length, cavity 14 has preferably at least twice the cross sectional area of the upper passage 14a leading into the internal chamber, and in the example shown the maximum cross section at the top of cavity 14 is about four or five times the cross section of passage 14a. Circulating fluid leaves the cavity throu h nozzles 18 and 19 which open directly to the cavity. Fluid velocity within the nozzles is relatively high but the nozzles may be made of hard metal alloy and are replaceable when unduly worn.

The rotating cutters are mounted on the shank by means of inclined pin 20. The pin is mounted on the shank by passing through an opening in plate 15 which is machined to a press fit with the pin so that the bearing pin firmly engages the shank plate. The pin then extends on through the side wall of the shank to which it is fastened by welding and then the end of the bearing pin is cut off and ground to conform to the external configuration of the shank.

The cutter mounting portion of pin 20 extends outwardly and downwardly from the shank plate 15 so that the pin axis BB makes an acute an le with the vertical axis AA of the shank and extends downwardly and outwardly from the shank axis. The two axes AA and BB preferably intersect substantially at the position shown. The acute angle between axes AA and BB is preferably approximately 66 or, in other words, axis BB lies at approximately 66 to the vertical when the bit is in normal drilling position.

Bearing pin 20 is threaded at 22 to receive bearing plate 23 which is screwed onto the bearing pin until the inner side of the plate firmly engages the face of plate 15 on the shank. The opposite or outer face of bearing plate 23 has an annular ball race consisting of a groove 24 of nearly semi-circular cross-section, as may be seen in Fig. 1.

Spaced slightly along pin 20 from plate 23 are a pair of relatively thin, disk-shaped cutters 26 and 27 which are mounted to rotate about the pin axis BB in parallel planes which are perpendicular to axis B -B. Each cutter 26 and 27 is provided around its perlphery w1th cutting elements 28 of suitable size and shape. Teeth 28 shown in Figs. 1 and 2 are intended to be merely illustrative of the different shapes of teeth that may be used as cutting elements and not necessarily limitative upon them. Teeth 28 may be provided with inserts or facing of tungsten carbide or other hard, wear resistant material in accord with usual practice.

Each of cutters 26 and 27 is provided on its two side faces with a concentric annular bearing race 24 which, when viewed in cross-section, is arcuate in outline and nearly semicircular.

Pin 20 is threaded at 30 in order to receive outer bearing plate 31 which has on its inner face an annular ball race 24 matching those already described. All races 24 have the same diameter about, and are concentric with, axis BB. The races are so arranged that there are three opposing pairs of races which may be filled with ball bearings 34 and thus provide means for rotatablv mounting the cutters on plates 23 and 31 and pin 20. Balls 34 riding in races 24 provide not OnlV radial bearings but also thrust bearings to support the cutters by and between the two stationary bearing plates 23 and 31.

In this construction, the central bore in the two cutters is preferably somewhat larger than the external diameter of pin 20 so that there is no direct engagement between the cutters and the cutter mounting pin for ra-- dial bearing. This construction is preferred since it eliminates wear on the pin which is affixed to the shank permanently. The pin does not need to be replaced or built up and resurfaced as would be the case if a journal type bearing were provided on the pin and the cutters were directly mounted to rotate upon such journal bearing. A further advantage of this construction is that the cutters are supported laterally at a substantial distance from their axis of rotation with the result that the cutters are held firmly against tilting, even though a considerable amount of wear occurs in the ball races.

The cutter assembly is held in place by locknut 36 hich is screwed onto the end of pin 20 threaded at 37. Threads at 30 and 37 are of opposite hand so that locknut 36 and bearing cap 31 are rotated in opposite directions to remove them or place them on pin 20. By welding the locknut to bearing plate 36 after the bearing and cutters are completely assembled in position, a locknut holds the bearing cap against backing oif the pin.

Cutter 26 is termed the gage cutter since the size of this cutter is a primary factor in determining the size of the hole drilled; and also the diameter of this cutter is equal to the nominal diameter or size of the drill bit. It is the cutter closer to the shank. The other cutter 27 is more remote from the shank and it is termed the lead cutter. Cutter 27 has a smaller diameter than cutter 26. There is no fixed ratio between the diameters of these t o cutters but both are designed to have the extreme tips of their cutting elements lying substantially on a vertical arc with its center at the intersection of axes AA and BB and having a radius slightly greater than the radius of the gage cutter. As typical of actual dimensions found practically successful, a gage cutter having an overall diameter of 12 inches mav be used with a lead cutter having an overall diameter of 10% inches.

As viewed in Fig. l, the two cutters are mounted non-symmetricallv upon the shank. Cutter 27 is disposed substantially entirely at one side of the shank axis AA while cutter 26 intersects the shank axis in its lower half so that the major portion of the gage cutter lies at the same side of the shank axis as does cutter 27. The location 40 of engagement of the cutting elements of cutter 27 with the earth formation at the bottom of the hole is offset from the shank axis by a small amount. The direction of this ofiset is such that position 40 is spaced from the longitudinal shank axis AA toward the same side at which cutter 27 is located with respect to the shank axis. Gage cutter 27 contacts the earth formation at the bottom of the hole at a position at the opposite sides of the shank axis. The spacing between the shank axis and the contact 40 at the bottom of the hole of cutter 27 is substantially less than the spacing between the shank axis and the corresponding point of contact 41 of cutter 26, as may be seen by reference to Fig. 1. With cutter of the dimensions referred to above, the oifset between axis A--A and location 40 may typically be approximately inch.

As a result of numerous experiments it has been found that the hole actually drilled by a bit with cutters of these dimensions is approximately 12% inches in diameter. Thus the diameter of the drilled hole exceeds the nominal size of the bit which is the diameter of the gage cutter, or 12 inches, by approximately twice the offset between the longitudinal shank axis and the contact of the lead cutter with the formation at the bottom of the hole. Actually, the axis CC of the drilled hole passes substantially through the point 40. From these facts it is deduced that when drilling, the drill bit tends to revolve not about its own longitudinal axis AA but about some other axis, such as axis CC, which becomes the axis of the hole being drilled. The distance between these two axes, which are parallel to each other, is determined by the dimensions of the drill bit, and chiefly by the offset of the bottom of the lead cutter with respect to the shank axis. The result is an over-size hole.

Rotation of shank by drill stem 12 in a clockwise direction, viewed from above, causes the two cutters to roll over the earth formation. The type of cutting elements shown in the drawings are particularly suited to relatively hard formations and break up the formation by a criss-cross cutting action. There is no tendency for the teeth to track, that is to enter the imprints of preceding teeth and so eventually have little cutting efiiciency. The cutters revolve in a clockwise direction about pin 20 when viewed as in Fig. 2. Since the diameter of the hole is larger than the diameter of the cutters, they are in cutting engagement with the formation over only about one-fourth of their periphery. This contact is approximately as shown in Fig. 2.

The present invention is not limited to particular spacing between contact position 40 and axis AA; it may be greater or smaller than mentioned above. Bits have been successfully tested with an offset of only /8 inch producing a hole that was nearly inch over-size.

Since the cutter 27 is inclined upwardly and away from axis AA, the spacing between contact position 40 tends to increase as the cutters wear. Thus the reduction in size of the gage cutter, which reduces the hole size, is compensated for to some extent by the increase in the offset which tends to increase the hole size.

It will be realized that the relationship between the cutters and the actual ground surface is somewhat idealized in the drawings. The bottom of the hole is rough with numerous minor elevations and depressions which are not shown in the drawings and the outline of the hole drilled is represented in ideal form by a single smooth line.

It is preferable to place one or more jets 19 at the bottom of the shank as close as possible to the bottom of the cutters in order to direct circulation fluid around teeth 28 at the bottom of their path and to flush cuttings olf the bottom of the hole, thus keeping the cutters always in engagement with uncut portions of the formation. One or more jets 18 are located above the cutters in order to direct fluid against the cutting elements at or near the top of their path for washing off any cuttings that may adhere to them and thus maintain the cutting elements at full efficiency.

Having disclosed a preferred typical embodiment of my invention, it will be apparent that modification in the various parts of my improved drill bit may be made without departng from the spirit and scope of my invention. Consequently, it is wished that the foregoing be considered as illustrative of, rather than limitative upon, the appended claims.

I claim:

1. In a rotary drill bit, the combination comprising: a shank adapted for attachment to a drill stem for retation thereby; an inclined cutter mounting pin mounted on the shank; and a pair of relatively thin, disc-shaped cutters mounted coaxially and side by side to rotate about the pin in parallel planes, each cutter having cutting elements about its periphery; one of said cutters lying substantially at one side of the longitudinal shank axis and engaging the earth formation at the bottom of the drilled hole at a position spaced toward said one side from the longitudinal shank axis spaced from and parallel to said shank axis and to drill a hole with its central axis passing substantially through said position fit 1engagement of the one cutter with the bottom of the 2. In a rotary drill bit, the combination comprising: a shank adapted for attachment to a drill stem for rotatlon thereby; an inclined cutter mounting pin mounted on the shank; and a pair of relatively thin, disc-shaped cutters mounted coaxially and side by side to rotate about the pin in parallel planes, each cutter having cutting elements about its periphery; the two cutters engaging the earth formation at the bottom of the drilled hole at opposite sides of the longitudinal shank axis, the cutter more remote from the shank projecting downward below the other cutter to establish the central axis for the hole being drilled parallel to but oflfset from the longitudinal shank axis.

3. In a rotary drill bit, the combination comprising: a shank having a longitudinal axis and adapted for attachment to a drill stem for rotation thereby; cutter bearing means carried by the shank establishing an inclined axis; and a cutter assembly comprising only a lead cutter and a gauge cutter 'mounted coaxially side by side on the bearing means to rotate in parallel planes about said inclined axis, both cutters being disc-type cutters with spaced peripheral teeth; the lead cutter being substantially at one side of the longitudinal axis of the shank and engaging the earth formation at the bottom of the hole to establish an axis of rotation of the bit at said one side of and offset from and parallel to the longitudinal shank axis, and the gauge cutter engaging the earth formation at the bottom of the cutter at the opposite side of the shank axis and spaced from the axis of rotation of the bit.

4. In a rotary drill bit, the combination comprising: a shank having a longitudinal axis and adapted for attachment to a drill stern for rotation thereby; cutter hearing means carried by the shank establishing an inclined axis; and a cutter assembly comprising only a lead cutter and a gauge cutter mounted co-axially side-by-side on the bearing means to rotate in parallel planes about said inclined axis, both cutters being disc-type cutters with spaced peripheral teeth; the lead cutter being substantially at one side of the longitudinal axis of the shank and engaging the earth formation at the bottom of the hole to establish an axis of rotation of the bit at said one side of and offset from and parallel to the longitudinal shank axis, and the gauge cutter being of larger diameter than the lead cutter with its greatest horizontal diameter spaced from said axis of rotation at the side away from the longitudinal shank axis.

5. In a rotary drill bit, the combination comprising: a shank having a longitudinal axis and adapted for attachment to a drill stem for rotation thereby; an inclined cutter mounting pin mounted on the shank; and a cutter assembly mounted on the pin to rotate about the inclined pin axis. said assembly including two side-by-side co-axial, disc-like cutters each having cutting elements around its periphery, said cutters rotating in parallel planes in close proximity to each other and being of sufficiently large diameter and so disposed that the cutting elements engage the earth formation on the downwardly moving side of the cutters and are disengaged from the earth formation on the upwardly moving side of the cutters to cut a substantially hemispherical bottom to the hole being drilled; both of said cutters being substantially at one side of the longitudinal axis of the shank and one of said cutters engaging the earth formation at the bottom of the cutter at a position substantially on the axis of the drilled hole and spaced from the shank axis toward said one side, and the other of said cutters intersecting the shank axis and engaging the earth formation at the bottom of the cutter at a position spaced from the shank axis oppositely to the said one cutter.

References Cited in the file of this patent UNITED STATES PATENTS 939,559 Seng Nov. 9, 1909 1,238,707 Bardeen Aug. 28, 1917 1,374,867 Wadsworth Apr. 12, 1921 1,388,497 Wadsworth Aug. 23, 1921 1,974,756 Seifert Sept. 25, 1934 2,133,022 Fisher Oct. 11, 1938 2,151,347 Fisher Mar. 21, 1939 2,191,699 Stephens Feb. 27, 1940 

